Hitherto, a foam of phosphoric acids has been suggested as an inorganic foam that can be produced under room temperature and ordinary pressure (see, for example Japanese Patent Publication No. 56-36145).
The foam described in this published official gazette is obtained by stirring and mixing phosphoric acids such as metal phosphate and blowing agent such as multivalent metal carbonate etc., and subjecting the mixture to foaming and curing. Since this foam has the following characteristics, it is applicable for not only a fixed shape material such as a panel etc. but also not-fixed shape filler for filling an opening portion, and, therefore, this material can be regarded as the excellent material that has not previously existed.
(1) The obtained foam is excellent in non-combustibility and fire proof property. PA1 (2) In the production of the foam, the control of specific gravity in a wide range can easily be conducted. PA1 (3) This foamable composition has the self blowing property. PA1 &lt;1&gt; An inorganic-organic composite foam having a foam structure made from phosphoric acids (a) and a blowing agent for phosphoric acids (b) and improved in brittleness by an urethane prepolymer having NCO groups (c). PA1 &lt;2&gt; The above mentioned foam further comprising an inorganic filler (d). PA1 &lt;3&gt; A process for the production of an inorganic-organic composite foam by foaming and curing by mixing each component, of phosphoric acids (a), a blowing agent for phosphoric acids (b), urethane prepolymer having NCO groups (c), water and, if necessary, an inorganic filler (d).
However, since the foam of phosphoric acids is a completely inorganic material, it has shortcomings. That is, it is brittle, and so just a little force can break foams and the broken foam cannot be recovered. Especially, when a big panel having low specific gravity is produced, there are following problems, for example, the surface is broken by only being touched; and further, the panel strength is too weak for the panel to be carried out. Consequently, such foam is far from a practical material.
As a means for improving such shortcomings of the foam of phosphoric acids, the method in which a resin emulsion such as SBR etc. is added to the composition is suggested (see, for example, JP-6-24869 A).
In this method, by adding resin emulsion to an extent that does not damage the excellent non-combustibility and heat resistance property that are the distinctive features of the foam of phosphoric acids, the strength of the foam is enhanced, and a practical material can be produced even from a foam having a high blowing ratio.
Although the strength of the foam of phosphoric acids can be improved drastically by adding resin emulsion, it is difficult to sufficiently improve the brittleness of the foam having a high blowing ratio, since this foam is an inherently brittle material. Moreover, it is further difficult to obtain a foam having a flexibility and rebound resilience like an urethane foam or a styrene foam.
The present inventors have intensively investigated in order to improve the above mentioned problems and obtained a foam using an urethane prepolymer having NCO groups that has reactivity and elastic property unlike the above mentioned resin emulsion.
Moreover, as a result of the investigation, the present inventors found that even if a foam having a high blowing ratio is produced by using this prepolymer, it exhibits the flexibility and rebound resilience as excellent as those of soft urethane foam although the obtained foam is inorganic-organic composite foam. This blowing ratio can be adjusted from soft to hard, and the brittleness can be improved remarkably in both the soft case and the hard case.
In other words, it is an object of the present invention to provide an inorganic-organic composite foam having non-combustibility and heat resistance, having a structure of an inorganic foam, with the brittleness remarkably improved by a reactive elastic polymer, and to provide a process for the production of the inorganic-organic composite foam, capable of producing the foam under conditions of room temperature and ordinary pressure.